Data communication standards and communication protocols are well known, widely used, and wide spread. Such standards provide the basis for various electronic devices to be able to communicate with each other. Certain communication standards have been in place since the 1970s and, due to their flexibility and ease of use, are still extensively used today in digital and analog communications between devices.
One such communications standard is the Modbus protocol. The original Modbus interface, created in late 1970s, operated on the RS-232 standard, with later interfaces was operated and running on the RS-485 standard. Because of the flexibility of the Modbus protocol, including the ability for it to be implemented and use by computer processors as well as intelligent sensors, the Modbus communications protocol developed into widely used standard that is still in use today. Indeed, because of the prevalence of the Modbus protocol, its use will likely continue for many years to come.
Modbus is a master device/slave device communications protocol that provides for the master device to request or initiate a message and the slave device to response or reply to the master device message. In data transmission, the Modbus communications are predominantly reading and writing of data from one register in a device to another register in one or more other devices. One of the strengths of the Modbus communications protocol is that the format of the data being transmitted is not limited by the protocol. That is, Modbus works on most any data format determined or set by the master and slave devices so long as the data formats are compatible.
There in is one of the limitations of the Modbus protocol: while there is substantial flexibility in usage of the Modbus protocol, there are often problems with interoperability between devices storing, retrieving and requesting different data formats. More particularly, while a slave device may have as a native data format floating point data, a request may come from a master device seeking data for a register with a 32-bit integer format. Other formats widely used for sensors include 16-bit integer format. Where multiple master and slave devices are communicating, the efficient inter-communication between such devices may be hindered if not prevented.
Systems have been designed for communication protocols. For example, U.S. Pat. No. 7,443,886 (the “'886 patent”), issued to Gross for a Communication Protocol System and Method, discloses a specific expanded protocol having a data packet, a control byte, and a checksum byte. The control byte of the protocol further includes several bits to identify (a) the address of a slave controller, (b) the data type being transmitted, (c) the source of the data, (d) whether data is included in the data packet, (e) the state of the master controller, and (f) the run/stop state of the master controller. The '866 patent does not however include any process to convert the format of the data packet being transmitted.
Another design for Modbus communications protocol in shown in U.S. patent application Ser. No. 11/689,513, Publication No. US 2008/0235420, by Wei (the “'513 application”), for a Method Of Detecting Master/Slave Response Time-Out Under Continuous Packet Format Communications Protocol. The disclosed method in the '513 application provides for the continuous sending of Modbus requests to a slave device through a detection device and to record each Modbus request sent time, and to have the slave device provide back to the detection device a response for each Modbus request. Calculations are then used to determine the precise response time-out of the slave device. As with other known prior art, the '513 application does not include any processing of the data packet transmitted to be able to convert the format of the data transmitted.
What is needed is a Modbus communications protocol that allows the master device to recall data from a slave device, where the data is stored in the slave device in the slave device's native format, and then allows for converting the data to another format based upon the Modbus register address protocol. What is also needed is a communications protocol that allows a master device to write data to a slave device, where the data format is to be converted to the slave device native format based upon the register address protocol. Such a Modbus communications protocol and method and system have not been created or recognized in the communications field.